The Internet is a convenient platform for people to exchange information. For example, a person seeking an answer to a question can post the question on the Internet by, e.g., sending an email message to his or her friends. Another person who receives the email message can answer the question by replying to the email message. There are multiple issues with this question-answer model. First, if the questioner does not know which friend(s) may be able to answer the question, he or she may have to send the question to a large number of friends or acquaintances, making it difficult to protect his or her privacy. This approach could also lead to email spamming on the receiving end of the question. Second, even if the questioner receives multiple answers to his or her question, he or she may find it quite challenging to tell which answer is the most credible without reading all of the answers.